In Biology organisms are organized (in descending order) into kingdoms, phylum, class, order, family, genus and species. In elementary biology the highest level is the kingdom.
No, because organisms are made up of organs, and, in turn, are components of ecosystems. The most inclusive biological level would probably be the entire biosphere.
domain
Domain.
The simplest level of organization as far as taxonomy goes would be the most inclusive one; a domain. If you are asking in terms of things such as organisms, it would be the smallest, the cell.
The United Nations is the international organization that is the most inclusive, has the most members, and has as a primary goal the maintenance of international peace and security.
domain
Species.
cell
The cell which is the basic unit of life
A cell.
In the modern organization of taxa, or scientific classification, the first level is the species. This is the most specific level.